This is the application of the Division of Neonatology at the University of Utah to continue in the Cooperative Multicenter Neonatal Research Network (NRN). The NRN objective is to conduct rigorous clinical research in the care of high-risk (particularly low birth weight) newborn infants, by providing sufficient diverse patient availability to answer important clinical questions in a timely, powerful and generalizable manner. Our NICUs remain well positioned to further these objectives. Specific strengths that the Division offers include: 1. Productive contributions to the Network during the 2006 cycle. 2. More than 2,000 admissions to our NICUs and over 9,500 on-site deliveries annually, with demographic mix different from the rest of the NRN. 3. A collaborative and productive relationship with our Division of Maternal Fetal Medicine, an exemplary participant in the NICHD Maternal Fetal Medicine Network (MFMU) that shares data and resources with us. Our continued participation in the NRN will benefit both networks. 4. Numerous other available resources remain: a) Utah Population Database, a unique resource to investigate genetic bases of newborn pathologic phenotypes; b) University of Utah CCTA and associated core facilities; d) Pediatric Pharmacology Program; e) interaction with multiple other research networks now under the rubric of the new University Institute for Woman and Child, including (but not limited to) the Pediatric Heart Disease Clinical Research Network, Pediatric Emergency Care Applied Research Network, the National Children's Study (Salt Lake County is a Vanguard Location and the University Department of Pediatrics is a Vanguard Center), the MFMU, and the NRN. To show how these resources can be used to answer important questions in low birth weight infants, we propose a study testing the hypothesis that thyroxine treatment of VLBW infants >7 days old with transient hypothyroxinemia will result in improved survival without neurodevelopmental impairment at 18-22 months. In summary, this application presents our continued commitment to further the clinical research mission of the NICHD NRN.